The present invention relates generally to systems and methods for suppressing machinery fires, and more particularly to an economical method and lightweight system for mitigating fires in machinery enclosures utilizing intumescent materials.
Aircraft engine nacelles and other housings for hot operating machinery may also enclose fluid lines on the exterior of the machinery that provide flammable fuel, oil or hydraulic/brake fluid to the operating machinery. The enclosures are typically ventilated with forced airflow (by fan or free air stream) to prevent accumulation of flammable vapors and to provide some cooling to the machinery. In a typical fire scenario, a ruptured fluid line leaks flammable fluid onto the hot machinery resulting in a fire. The ventilation airflow continues to support the fire and directs the flame downstream. An upstream extinguishing system may be activated to extinguish the fire, but because of rapid dilution by the ventilation airflow, short residence time of the extinguishant near the fire and robustness of the flame, many fires are not extinguishable with the limited quantity of extinguishant available in weight sensitive applications such as aboard an aircraft. After initial extinguishment, the fire may re-ignite because of continued fluid flow onto the hot machinery surface combined with replenished airflow across the hot surface after the extinguishant is exhausted. Replacement chemicals for Halons previously having widespread use in extinguishers are substantially less effective than Halons. Existing systems therefore have limited success or require extinguishant quantities and hardware that are impractical in many machinery applications.
The invention solves or substantially reduces in critical importance problems in the prior art by providing a system and method for suppressing fires in machinery spaces by strategic placement of intumescent materials within the machinery space. Intumescent materials are substances that react chemically when impinged by intense heating sources such as fire. The reactions change both chemical makeup, structure and volume of the material as a means of accommodating the thermal energy applied. The responses of the intumescent materials protect the structures on which they are applied, by dissipating heat or providing an insulative barrier to prevent thermal damage to the internal structure. The intumescent materials typically initiate endothermic chemical reactions when impinged by a heat source, which extract and process the heat applied to sustain the reaction, as opposed to raising the temperature of the material. The intumescents may also physically swell dramatically in size (2 to 50 times the original thickness), and form an insulative porous char on the outer surface. For example, a 1 mm layer of intumescent of about 1.5 g/cm3 density may expand to form a non-cumbustible layer 2 mm to 50 mm thick, with a density of 0.7 g/cm3 to 0.03 g/cm3. Intumescent formulations are generally composed of three active classes of ingredients, including an acid source, a carbonific source and a spumific agent. A series of chemical and physical events combine to control intumescence. As the virgin material is exposed to heat, the temperature rises, releasing an inorganic acid. In the presence of an inorganic catalyst, the acid is thought to react with carbon compounds forming a melt. An endothermic reaction subsequently releases gases that form bubbles, resulting in an intumescent foam that solidifies into a multicellular char. Cellular voids are filled with gases, causing the char to act as an insulating barrier. The gases are principally CO and H2O, although small amounts of CH4 and H2 are also found. The char will not burn but will reject heat by radiating it away. As flame heating continues, this process occurs in depth, layer after layer, until the material is depleted or the incident heat flux is reduced. The final form of the intumesced layer acts as an insulating barrier, which protects the underlying material from flame heat flux. Intumescent material formulations are highly proprietary and unique to various manufacturers, and include latex, epoxy and oil based varieties, as well as some mastics or caulks. Some formulations include ceramic fibers (Hamins, 1998, xe2x80x9cEvaluation of Intumescent Body Panel Coatings in Simulated Post-Accident Vehicle Fires,xe2x80x9d Report #NHTSA-1998-3588-24; NISTIR 6157). If a fire occurs, the intumescent material swells upon heating to several orders of magnitude of its original thickness and blocks the air flow in the vicinity of the fire, depriving the fire of oxygen and facilitating extinguishment. The intumescent material can be applied as a lightweight narrow thin strip or as one or more rings on the machinery exterior, and may preferably be located to swell against the enclosure at locations where clearance is minimal. In this manner, a series of fire walls can be formed using a minimal quantity of intumescent material. The effectiveness of any other extinguishing system used on the machinery is improved because the intumescent material weakens the fire and reduces air dilution of the extinguishant. The invention may, however, obviate the need altogether for conventional extinguishment systems in machinery applications. The unexpanded intumescent material does not significantly impede airflow around the machinery during normal operation.
The invention finds utility in applications where extinguishing systems may not be justified, such as in unmanned aerial vehicles. The invention may also be used in aircraft engine nacelles and other bays where flammable fluids are present, in armored vehicle engine compartments, battlefield equipment or electronic trailers, naval ship machinery enclosures, stationary turbines, and marine engines, buses and other automotive transportation equipment, fixed generator and compressor units, power equipment trailers, petrochemical facilities, and other applications where liquid-fueled, oiled or hydraulically controlled equipment is operated. The use of intumescent material according to the invention requires no power or periodic maintenance and is highly reliable.
It is therefore a principal object of the invention to provide system and method for suppressing machinery fires.
It is another object of the invention to provide a fire suppression system and method for the engine compartment of a vehicle.
It is another object of the invention to provide a lightweight system for suppressing machinery fires.
It is another object of the invention to provide a machinery fire extinguisher system that does not impede airflow around the machinery during normal operation.
It is another object of the invention to provide a reliable machinery fire extinguisher system having no operational power or periodic maintenance requirements.
It is yet another object of the invention to provide system and method for suppressing machinery fires utilizing intumescent materials.
It is a further object of the invention to provide method and system for suppressing fires in machinery spaces that do not use conventional, environmentally harmful extinguishants.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, the mitigation of fires in machinery enclosures is achieved by strategic placement of thin narrow strips of intumescent material within the ventilated space between the machinery and a housing enclosing the machinery, whereby, in the event of a fire, the resulting flame contacts the intumescent material causing it to swell and to effectively block air flow through the ventilated space.